The present invention relates generally to a superconducting magnet and more particularly to a cooling system for such a magnet.
Superconducting magnets may be used for various purposes, such as to generate a uniform magnetic field as part of a magnetic resonance imaging (MRI) diagnostic system. MRI systems employing closed or open superconductive magnets are used in various fields such as medical diagnostics. Open magnets typically employ two spaced-apart toroidal-shaped superconducting coil assemblies, while closed magnets typically employ a single solenoidal-shaped superconducting coil assembly. The superconducting coil assembly includes one or more superconductive coils which are wound from superconductive wire.
Some superconductive magnets are cooled by a cryocooler coldhead (such as that of a conventional Gifford-McMahon cryocooler) which is mounted to the magnet. If there is an electric power outage or if the cryocooler otherwise malfunctions (or even has its performance degrade over time), the superconducting magnet will heat up and quench (i.e., lose its superconductivity). Also, although conventional cryocoolers can achieve low temperatures in the range of 3.5 to 4.0 Kelvin, their cooling capacity is modest, and a typical cryocooler-cooled MRI superconductive magnet may take up to a week or so to reach superconductive temperatures during start-up or during recovery from a quench. Other superconductive magnets are cooled by liquid helium placed inside the magnet, with such liquid helium boiling off as gaseous helium during magnet cooling and with such gaseous helium typically escaping from the magnet to the atmosphere. Such placement of the liquid helium inside the magnet is incompatible with compact magnet designs. What is needed is an improved cooling system for a superconductive magnet. Further, the cooling system must be compatible with compact superconductive magnet designs.